The most salient result is the appearance of DNA fragmentation in absence of necrosis when the mesencephalic neuronal cultures are deprived of neurotrophic factors. In this condition, the exposure to Pb2+ increases the appearance of neuronal necrosis. In contrast, the exposure of cerebellar granule cell cultures to Pb2+ increases the density of DNA fragmentation. This process is accelerated when the availability of neurotrophic factor is decreased.